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Author Topic: PDF images for photoresist PCB board making  (Read 12298 times)

2E0ILY

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PDF images for photoresist PCB board making
« on: September 17, 2017, 01:15:55 AM »

I had a kind guy in Germany offer to convert photos of three existing mint, populated PCB boards that are the same as three others in an obsolete power supply that have suffered damage over the years from repairs and lifted tracks. the pdf's looked great and were, when printed "actual size" absolutely spot on. But the images from the pdf whether on semi opaque "tracing" type paper or clear acetate sheet are not fully opaque, unlike some commercial ones that i found in my secondhand UV box when I bought it. I used an oldish HP B&W laser printer here at home, then sent the pdf files to a commercial printer who used some sort of plotter to print to acetate, but still the tracks are only semi opaque, and when I expose photoresist board the pads and some tracks seem to have had patches exposed to some UV so they develop at different times to other regions. this the affects etching....

Could someone kindly look at the pdf's and say if it's an issue with the density of the black in them, as they sort of appear a bit greyish... I have etched boards in the past with photo resist and had no great issues, but these are being a pain! It may be nothing to do with the density of the tracks, it may be my techniques, but I thought i should start at the beginning as I am not sure just what magic he used to go from photos of the tracks on a populated board to pdfs. I can drill the finished boards on a mill with a DRO, all the components are leaded, save 2 small IC's that I will socket. I can use the DRO to perfect, accurate hole spacing for them. But first I need usable boards! The images in pdf form are at http://www.gatesgarth.com/traces.pdf I am working with Page 4 the traces only, mirrored.

Thanks
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Best regards, Chris Wilson.

WD4HXG

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RE: PDF images for photoresist PCB board making
« Reply #1 on: September 17, 2017, 03:46:51 AM »

Shades of gray with computer B&W printers is achieved by
changing the dot density. They do not print pixel for pixel.
Rather they print a screen pixel on the page by arraying
multiple printer pixels or dots. HP has a paper describing
the process in their app notes on printing quality. Thus if
the printer uses a 3 by 3 array of printed dots to represent
a single pixel, 9 printed dots would be pure black in their
scheme and no printed dots would be pure white.

I suggest you find someone with an image graphics program
such as Photoshop or you can try GIMP. Open the image file
you have. Then use 'CTRL A' to select all printed pixels on the screen.
Look at the characteristics. I forget if Photoshop uses an
RGB value of 0,0,0 or 255,255,255 to represent all black but
I am willing to bet your image is using an RGB value somewhere
between the two. If that is true, then try changing the color
value used to the extreme 0,0,0 or 255,255,255 whichever
represents pure black and then save the file. Now print it
and your density may improve. Another thing you can do
is to expand a small area of the print to display on the entire
screen till you can see the individual image pixels. You will
likely see the screen pixels are a shade of gray as opposed
to black.

73

Chuck
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G4AON

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RE: PDF images for photoresist PCB board making
« Reply #2 on: September 18, 2017, 01:41:02 AM »

Chris, producing boards at home using UV light boxes was a 1980s idea. It is far easier to use a laser printer and heat transfer paper. The paper is shiny on one side, you print a reverse image on that side and iron it onto plain copper print board. The paper is widely available on eBay, searching for "pcb heat transfer paper" will bring up the stuff, it's yellow in colour and costs around 15GBP for 100 x A4 sheets. You could probably directly use those PDF images using the yellow paper. I use the stuff extensively when building my home brew projects, some of the PCBs can be seen at: http://www.qsl.net/g4aon/g4aon_ssb_tx/

Also you can "clean up" images of old PCB traces in PCB design programs that allow you to use a scanned image in the background, which you then use to create a new layout by "joining up the dots" as it were. One such program, that I use, is Sprint-Layout (http://www.abacom-online.de/uk/html/sprint-layout.html).

73 Dave
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2E0ILY

  • Member
  • Posts: 237
RE: PDF images for photoresist PCB board making
« Reply #3 on: September 18, 2017, 03:10:19 AM »

Shades of gray with computer B&W printers is achieved by
changing the dot density. They do not print pixel for pixel.
Rather they print a screen pixel on the page by arraying
multiple printer pixels or dots. HP has a paper describing
the process in their app notes on printing quality. Thus if
the printer uses a 3 by 3 array of printed dots to represent
a single pixel, 9 printed dots would be pure black in their
scheme and no printed dots would be pure white.

I suggest you find someone with an image graphics program
such as Photoshop or you can try GIMP. Open the image file
you have. Then use 'CTRL A' to select all printed pixels on the screen.
Look at the characteristics. I forget if Photoshop uses an
RGB value of 0,0,0 or 255,255,255 to represent all black but
I am willing to bet your image is using an RGB value somewhere
between the two. If that is true, then try changing the color
value used to the extreme 0,0,0 or 255,255,255 whichever
represents pure black and then save the file. Now print it
and your density may improve. Another thing you can do
is to expand a small area of the print to display on the entire
screen till you can see the individual image pixels. You will
likely see the screen pixels are a shade of gray as opposed
to black.

73

Chuck



Thanks for the detailed reply Chuck. I hadn't realised there was a trial version of Photoshop, so I have downloaed it and opened the pdf file in it. I selected the mirror images on page 4 and pressed CTRL-A I then set RGB to max levels and saved as another pdf. Whilst I THINK the traces are blacker, they now have castellated edges and look blurry. Can you suggest what I have done wrong please? Should I save as another format? Thanks.
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Best regards, Chris Wilson.

2E0ILY

  • Member
  • Posts: 237
RE: PDF images for photoresist PCB board making
« Reply #4 on: September 18, 2017, 03:11:46 AM »

Chris, producing boards at home using UV light boxes was a 1980s idea. It is far easier to use a laser printer and heat transfer paper. The paper is shiny on one side, you print a reverse image on that side and iron it onto plain copper print board. The paper is widely available on eBay, searching for "pcb heat transfer paper" will bring up the stuff, it's yellow in colour and costs around 15GBP for 100 x A4 sheets. You could probably directly use those PDF images using the yellow paper. I use the stuff extensively when building my home brew projects, some of the PCBs can be seen at: http://www.qsl.net/g4aon/g4aon_ssb_tx/

Also you can "clean up" images of old PCB traces in PCB design programs that allow you to use a scanned image in the background, which you then use to create a new layout by "joining up the dots" as it were. One such program, that I use, is Sprint-Layout (http://www.abacom-online.de/uk/html/sprint-layout.html).

73 Dave

Hi Dave, thanks for that, a few people have mentioned heat transfer direct to the PCB, I will give it a go. is an iron sufficient, as some seem to use a laminating machine with heated rollers?
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Best regards, Chris Wilson.

G4AON

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  • Posts: 2178
RE: PDF images for photoresist PCB board making
« Reply #5 on: September 18, 2017, 03:44:59 AM »

An ordinary iron works just fine. I use a new wooden chopping block under the board. The paper will stick to the PCB, take the hot paper/board and rinse under cold running water, then peel off the wet paper leaving the toner firmly stuck to the copper. Trying to peel off the paper while it's hot can result in the toner lifting. Any gaps can be touched up with an etch resist pen or with a cocktail stick and nail varnish. I get very few gaps.

73 Dave
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K8AXW

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RE: PDF images for photoresist PCB board making
« Reply #6 on: September 19, 2017, 09:54:49 AM »

Lacking a laser printer I have taken my layouts to my credit union where they will make as many copies as I want and adjust the density of the print to suit my needs.  Free!

Or, if you prefer, the bank you do business with will probably do the same.  Free!
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A Pessimist is Never Disappointed!

WD4HXG

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  • Posts: 396
RE: PDF images for photoresist PCB board making
« Reply #7 on: September 20, 2017, 06:12:05 PM »

Chris

I believe Photoshop's menu has a selection across the top for 'IMAGE'.
Click on it and scroll down to 'Image Size'. When it opens a small window
look at the number of pixels. It likely is 72 which is common on images
for magazines. Change it to 300. You can increase the number higher
but the file size may become unwieldy. Make sure the image dimension
does not change and then save it. Use a copy of the original file. I
believe that will address the ratty edges.

73

Chuck
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KA0HCP

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RE: PDF images for photoresist PCB board making
« Reply #8 on: September 21, 2017, 09:21:37 AM »

Stack multiple transparencies!  This will provide a more opaque image.

This has been a common method for decades.  Print several copies of the transparency; carefully align (register) them, tape together at the edges then lay on the photo sensitive plate.
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KA0HCP, ex-KB4QAA Relocated to Ks. April 2019.
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